HS4. 71GT not starting after romoving carbs : MGB & GT Forum : The MG Experience

HS4. 71GT not starting after romoving carbs #1
Markp61 Mark Pasquill MARION, MA, USA Sign in to contact 1959 MG MGA 1500 1971 MG MGB GT 2022 Ford Mustang "Beast"	Topic Creator (OP) Apr 30, 2017 03:47 PM Top Contributor Joined 8 years ago 1,354 Posts

Let me start by saying I think I did something wrong hence the issue. Removed both carbs , heat shield and manifold. Cleaned and painted manifold and heat shield. Cleaned carbs externally. Took pictures before I started. But I must have done something wrong. Eventually it fires engine revs. When I press the throttle it does. Running rough when started. Lift throttle cable and it dies. I also do not see the pistons list now when lifting throttle cable. I must have disturbed something. Thought I had covered myself. New gaskets on heat shield, 3 per carb. It's s the engine reving to about 3k. Then I press the gas and it dies. Fuel pump ok. Bowls have fuel. Any idea what I may have screwed up

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Re: HS4. 71GT not starting after romoving carbs #2
dickmoritz Dick Moritz Philly 'burbs, PA, USA Sign in to contact	Apr 30, 2017 03:51 PM Top Contributor Joined 14 years ago 26,273 Posts

Choke linkage is on wrong. Turn it so it is "nuts up" and engage the little tangs at the outer ends of the choke linkage with the appropriate holes in the carb linkage. I suspect that your throttle linkage is on part of the high step of the fast idle cams on the choke linkage...

Dick

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Re: HS4. 71GT not starting after romoving carbs #3
ozieagle Herb Adler Geelong Victoria, Australia Sign in to contact 1958 Wolseley 1500 "Wooly" 1966 MG MGB "Bl**dy B" 1995 Toyota Highlander "Hi Ace Van" 2022 MG ZS	Apr 30, 2017 03:56 PM Top Contributor Joined 13 years ago 15,857 Posts

IIRC the throttle lever, to which the cable attaches should be just below the choke connecting rod.

Herb

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Re: HS4. 71GT not starting after romoving carbs #4
Markp61 Mark Pasquill MARION, MA, USA Sign in to contact 1959 MG MGA 1500 1971 MG MGB GT 2022 Ford Mustang "Beast"	Topic Creator (OP) Apr 30, 2017 06:28 PM Top Contributor Joined 8 years ago 1,354 Posts

Dick I see what you mean re choke linkage. No excuses I just checked my pics. I put together same waybit came apart. My bad for not checking. Forgive me but don't understand what you mean te the throttle.

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Re: HS4. 71GT not starting after romoving carbs #5
dickmoritz Dick Moritz Philly 'burbs, PA, USA Sign in to contact	Apr 30, 2017 09:09 PM Top Contributor Joined 14 years ago 26,273 Posts

When the choke linkage is properly assembled, there are eccentric cams on both the front and rear carbs. There are screws on the underside of the throttle links that have springs around them. They should be in the vicinity of the cams on the choke linkage, but not touching when the choke knob is pushed in. When you pull the choke, these cams should rotate with the choke linkage, pushing on these fast idle screws, and it is this action that gives you a faster idle speed when the choke is engaged. In your bottom photo it appears that these screws may be touching the cams, which would hold the idle speed up much higher than normal...

Dick

In reply to # 3501136 by Markp61 Dick I see what you mean re choke linkage. No excuses I just checked my pics. I put together same waybit came apart. My bad for not checking. Forgive me but don't understand what you mean te the throttle.

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(Often wrong, but always certain)

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Re: HS4. 71GT not starting after romoving carbs #6
Markp61 Mark Pasquill MARION, MA, USA Sign in to contact 1959 MG MGA 1500 1971 MG MGB GT 2022 Ford Mustang "Beast"	Topic Creator (OP) May 1, 2017 06:06 AM Top Contributor Joined 8 years ago 1,354 Posts

Dick. Thank you. That makes sense. I need to get back into it at the weekend. I think I also have a leak on the rear carb between the spacer block and the carb. I can see and wipe a small amount of gas off the heat shield. Much appreciate the advice. I found some clearer pics on the site also so see what you are saying.

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Re: HS4. 71GT not starting after romoving carbs #7
33EJB Tim C LS, Eastern Ontario, Canada Sign in to contact 1969 MG MGB	May 1, 2017 07:41 AM Top Contributor Joined 12 years ago 3,245 Posts

Should look like this...

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Re: HS4. 71GT not starting after romoving carbs #8
Markp61 Mark Pasquill MARION, MA, USA Sign in to contact 1959 MG MGA 1500 1971 MG MGB GT 2022 Ford Mustang "Beast"	Topic Creator (OP) May 1, 2017 07:45 AM Top Contributor Joined 8 years ago 1,354 Posts

Thank you much appreciated

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Re: HS4. 71GT not starting after romoving carbs #9
Fidor Bruce G Glendale, CA, USA Sign in to contact 1970 MG MGB GT "Cannondale SuperSix Evo"	May 1, 2017 08:05 AM Joined 11 years ago 231 Posts

re leakage, double check the nuts and the gaskets holding the carbs to the manifold.

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Re: HS4. 71GT not starting after romoving carbs #10
naturbar Buz Natur Randleman, N.C., USA Sign in to contact 1973 Chevrolet Nova "Drag Race...anyone ?" 1977 MG MGB "Her B For Me" 1978 Toyota Pickup "Black Beauty"	May 1, 2017 09:26 AM Top Contributor Joined 12 years ago 2,068 Posts

First let me state up front that I am not an expert on SU carbs, however I have converted from a Weber to HS4's after a complete rebuild. I am going to make some observations (see attached pics).... I am certain those well versed in SU setups will pipe in to clarify any Faux Pas I make. Again the comments I am making are concerning the way I have my SU's set up per research I've done. it appears to me that your throttle cable may be maladjusted (pulling throttle open in resting position) causing a high rpm idle situation.. Take it all with a grain of salt and know that I am only trying to help. Best of luck on your endeavor. the first pic is my setup - the second pic is your setup.

Buz

Buz

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Re: HS4. 71GT not starting after romoving carbs #11
Markp61 Mark Pasquill MARION, MA, USA Sign in to contact 1959 MG MGA 1500 1971 MG MGB GT 2022 Ford Mustang "Beast"	Topic Creator (OP) May 1, 2017 09:30 AM Top Contributor Joined 8 years ago 1,354 Posts

Buz

Thanks, I agree it looks off, I found a few weird things, I,m no SU expert myself, hence, the chock, I put it back the way I found, to I copied the PO, silly me, should have known better

I also think I have a vacuum leak, which isn't helping either

Will be back at it this weekend

Regards

Mark

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